Thanks for the help. I think I am on the right track but am still running into a bit a difficulty :confused:.
To plug equation (3) into equation (2) do I first need to solve for theta? I am sorry but I am not completely clear on the set up for the direct substitution.
Thanks
Homework Statement
By direct substitution, show that equation (3) is a solution of the differential equation (2).
Homework Equations
(2) (d^2 θ)/(dt^2 )=-g/l θ (Second derivative of θ(t)=-g/l θ.)
(3) θ(t)=θ_0 cos(√(g/l) t)
The Attempt at a Solution
I...